1. Field of the Invention
This invention relates to the interconnection of electronic circuitry. In particular, the present invention relates to an optically coupled calibrator for use in calibrating transmitters, such as a two wire transmitter.
2. Description of the Prior Art
Since the discovery of electricity, electrical and electronic circuit components have been coupled by current carrying conductors to perform desired functions. The valence ring of these conductors' atoms are typically metallic and have one, two or three electrons. These electrons are called "free" electrons as the application of a very small voltage causes the electron to leave the atom, hence causing an electrical current. Typical conductors are copper, silver, gold, aluminum and others.
In recent times, electrical and electronic components have been coupled together by a light signal. Typically, these applications have used a light emitter, a light sensor, and an optical transmission means, such as a fiberoptic cable. As used in this patent application, the term "light" is not limited to visible radiation but rather includes electromagnetic radiation in the infrared, visible, and ultraviolet portions of the spectrum. Example of prior art systems of this type include the following patents.
In U.S. Pat. No. 3,493,760 to Hoadley, an electrical signal modulates a gallium arsenide light source and the light beam from the source is directed through aperatures in the shielded instrumentation package such as those used for weapons systems to a light sensitive diode which reproduces the electrical signal for use by the instrumentation circuit. This patent provides for transducer light isolation and does not solve the calibration problem for industrial transmitters.
In U.S. Pat. No. 3,346,811 to Perry et al. a device for sensing an electrical condition near a high voltage transmission line and transmitting the intelligence through a fiber optic dielectric device to a light signal receiving means near ground potential is described. This patent also describes transducer isolation by light signals.
U.S. Pat. No. 3,964,020 to Dickerson describes a high voltage system with self test circuitry. The self-test is a test of the communication links. This patent describes transducer isolation by light signals.
The prior art has shown the use of the light signals to provide isolation, however, as indicated in these prior art patents, the light isolation is provided between the signal sensing element and the electronics.